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Selective growth of InxGa1-xAs on a SiO2-mask patterned GaAs(001) substrate by molecular beam epitaxy (MBE) is reported. A simple model for selective growth is derived from the general rate equation of thin film growth. Based on this model, heteroepitaxial selective growth of InxGa1-xAs with x up to 0.07 is demonstrated at 595 °C, which is within the range of typical MBE growth temperatures for GaAs but is above the desorption temperature of In atoms from a GaAs surface. An incorporation rate of In atoms of about 0.22% for a Ga flux of 2.0×1013 atoms/cm2 s was measured at this temperature. The concentration of In atoms effectively incorporated into the InxGa1-xAs layer is linearly proportional to the supplied In flux in the range 0.7–9.2×1014 atoms/cm2 s. The extremely low, but finite, In incorporation is utilized for the growth of 5 nm thick InxGa1-xAs/GaAs quantum wells and ∼300 nm thick InxGa1-xAs layers. Together with selective growth, the surface morphology and optical properties of high-temperature grown InxGa1-xAs are characterized. [ABSTRACT FROM AUTHOR]

Room-temperature emission is observed as long as 3.26 µm in optically pumped type-I quantum well lasers on relaxed epitaxial layers grown by molecular-beam epitaxy. A superlattice is used to filter dislocations in the metamorphic buffer to reduce Shockley-Read-Hall losses. The longest wavelength emission of 3.45 µm from these structures is observed at 170 K, and the brightest room-temperature laser emits 0.5 W/facet peak power at 2.81 µm. It has a low threshold power density of 169 W/cm² and a differential quantum efficiency of 28%. The characteristic temperatures, T[sub 0] and T[sub 1], are 119 K and 171 K, respectively. Stimulated emission is observed in this sample at a maximum operating temperature of 370 K. [ABSTRACT FROM AUTHOR]

The authors investigate the etch modes of GaSb (100) through use of Arsenic (As2) based in situ etching. Three distinct etch modes result from temperature dependent in situ etching. The authors have used this in situ etch process on highly strained (In)GaSb quantum wells (QWs) and have studied the dependence of the in situ etching on substrate temperature and indium composition in the quantum well. The etched quantum wells are capped with an Al0.5Ga0.5Sb barrier and the photoluminescence properties are studied. The authors observe inhomogeneous broadening indicating the possible presence of quantum-sized features with different shapes and sizes. [ABSTRACT FROM AUTHOR]

We report the device characteristics of GaInSb/AlGaSb quantum well (QW) lasers monolithically grown on GaAs substrates by using an interfacial misfit (IMF) array. The IMF array localized at the GaSb/GaAs interface can accommodate the 7.8% lattice mismatch between GaAs substrates and GaSb buffer layers, resulting in the formation of a GaSb buffer with a very low defect density on GaAs substrates. Top-top and top-bottom metal contact methods are applied to the Ga0.9In0.1Sb/GaSb QW edge-emitting lasers monolithically grown on GaAs substrates for characterizing current–voltage ( I– V) and output power–current ( L– I) curves. The potential drop at the IMF array of ~0.7 V is elucidated by comparing I– V characteristics with these two contact methods. L– I characteristics and electroluminescence spectra shows room-temperature lasing at 1.83 μm from a 1.25-mm-long top-top contact device containing six-layer Ga0.9In0.1Sb QWs with a threshold current density ( J th) of 860 kA/cm2. This IMF technique will enable a wide range of lasing wavelengths from near- to mid-wavelength infrared regimes on a GaAs platform. [ABSTRACT FROM AUTHOR]

The authors report the device characteristics of GaInSb/AlGaSb quantum well (QW) lasers monolithically grown on GaAs substrates. The 7.8% lattice mismatch between GaAs substrates and GaSb buffer layers can be completely accommodated by using an interfacial misfit (IMF) array. Room-temperature lasing operation is obtained from a 1.25-mm-long device containing six-layer Ga0.9In0.1Sb/Al0.35Ga0.65Sb QWs at 1.816 μm with a threshold current density of 1.265 kA/cm2. The observed characteristic temperature and temperature coefficient are 110 K and 9.7 Å/K, respectively. This IMF technique will enable a wide range of lasing wavelengths from near-infrared to midwavelength-infrared regimes on a GaAs platform. [ABSTRACT FROM AUTHOR]

The authors report the optical characteristics of GaSb/GaAs self-assembled quantum dots (QDs) embedded in an InGaAs quantum well (QW). Variations in the In composition of the QW can significantly alter the emission wavelength up to 1.3 μm and emission efficiency. Lasing operation at room temperature is obtained from a 2-mm-long device containing five stacked GaSb QDs in In0.13Ga0.87As QWs at 1.026 μm with a threshold current density of 860 A/cm2. The probable lasing transition involves electrons and holes confined in the QW and QDs, respectively, resulting in a large peak modal gain of 45 cm-1. A significant blueshift of the electroluminescence peak is observed with increased injection current and suggests a type-II band structure. [ABSTRACT FROM AUTHOR]

The authors demonstrate a monolithic, electrically injected, vertically emitting GaSb/AlGaSb light emitting diode (LED) emitting at 1.6 μm comprised of a hybrid GaAs/GaSb-based structure. The LED is comprised of a GaSb/AlGaSb quantum well/barrier active region embedded within high index contrast GaAs/AlGaAs distributed Bragg reflectors (DBRs) using two interfacial misfit (IMF) arrays to relieve the strain induced from the high 8% lattice mismatch between the material systems. The first IMF is formed under compressive strain conditions to enable strain-free, defect-free deposition of GaSb active region directly on the lower GaAs/AlAs DBRs without need for thick buffer. The second IMF is formed under tensile conditions to enable the upper GaAs/AlAs DBRs on the GaSb active region. The device demonstrates a maximum output power of 3.5 μW. Initial diode optical and electrical characteristics along with IMF band structure are discussed. [ABSTRACT FROM AUTHOR]

We report, for the first time, temperature-dependent Hall data for holes in modulation-doped In0.2Ga0.8As/GaAs strained-layer superlattices. Samples with (compressive) planar strains of -0.5% to -1.2% in the InGaAs quantum wells were used, providing a range of configurations for the two (overlapping) sets of valence-band quantum wells derived from the bulk heavy- and light-hole bands. All samples exhibit transfer of holes into the InGaAs quantum wells at low temperature; however, the sample with the least strain shows evidence for gradual carrier freeze-out over a wide range of temperature. [ABSTRACT FROM AUTHOR]

We report the electrical chracterization of an InAs/AlAsSb quantum well heterostructure capacitor fabricated on material grown by molecular beam epitaxy. Hysteresis associated with electron storage was observed in the capacitance-voltage data from which we derived exponential charge decay constants of 50 s at 77 K. [ABSTRACT FROM AUTHOR]

Cyclotron resonance of the two-dimensional hole gas (2DHG) in the strained-layer quantum well structure of In0.20Ga0.80As/GaAs is observed in far-infrared transmission measurements made at 4.2 K. The cyclotron mass of the 2DHG in the In0.20Ga0.80As channel is (0.191±0.008)me for a 2D hole density p2D =8.5×1011/cm2. [ABSTRACT FROM AUTHOR]

We report the first continuous-wave (cw) photopumped operation of surface-emitting lasers comprising pseudomorphic InGaAs quantum wells. The lasers were grown by molecular beam epitaxy and incorporate epitaxial quarter-wave AlAs/GaAs mirrors surrounding an active region. In the active region, 50 Å InGaAs quantum wells are distributed with half-wave periodicity to center on cavity standing wave maxima. Lasing is observed from 78 to 250 K in the spectral range 920–950 nm, where the GaAs substrate is transparent. Thresholds were as low as 1.5×104 W/cm2, and overall (differential) output power efficiency was as high as 35% (85%) with up to 60 mW in a low divergence beam. Both periodic gain and biaxial compressive layer strain contribute to the reduced lasing threshold. The laser gain length is only 550 Å (11 quantum wells). The possibility of surface-emitting lasing in single quantum wells is discussed. [ABSTRACT FROM AUTHOR]

The critical layer thickness for InxGa1-xAs layers in InxGa1-xAs/GaAs single strained quantum wells (SSQW’s) and strained-layer superlattices (SLS’s) are investigated. Photoluminescence microscopy (PLM) images and x-ray rocking curves for two series of SSQW and SLS structures corresponding to many different layer thicknesses were obtained. We find that the PLM technique, which directly images dislocations and is sensitive to low dislocation densities, is much more suitable for determining the onset of dislocation creation. The x-ray technique can detect lattice relaxation by dislocations but only at relatively high densities of dislocations. Using the former technique, we determine critical thicknesses of 190 Å for SSQW’s and 250 Å for SLS’s with x≊0.2. These results are near the theoretical predictions of J. W. Matthews, S. Mader, and T. B. Light [J. Appl. Phys. 41, 3800 (1970)] (150 and 300 Å, respectively) and are much lower than results obtained by x-ray or other techniques which sense lattice relaxation. [ABSTRACT FROM AUTHOR]

We report accurate determination of the critical layer thickness (CLT) for single strained-layer epitaxy in the InGaAs/GaAs system. Our samples were molecular beam epitaxially grown, selectively doped, single quantum well structures comprising a strained In0.2Ga0.8As layer imbedded in GaAs. We determined the CLT by two sensitive techniques: Hall-effect measurements at 77 K and photoluminescence microscopy. Both techniques indicate a CLT of about 20 nm. This value is close to that determined previously (∼15 nm) for comparable strained-layer superlattices, but considerably less than the value of ∼45 nm suggested by recent x-ray rocking-curve measurements. We show by a simple calculation that photoluminescence microscopy is more than two orders of magnitude more sensitive to dislocations than x-ray diffraction. Our results re-emphasize the necessity of using high-sensitivity techniques for accurate determination of critical layer thicknesses. [ABSTRACT FROM AUTHOR]

A selectively doped, n-type, single strained quantum well (SSQW) structure, consisting of an 8-nm-thick In0.25Ga0.75As layer sandwiched between thick GaAs layers, has been grown by molecular beam epitaxy. Low-field Hall-effect measurements from 4 to 300 K and field-dependent magnetotransport measurements at 4 K show that conduction through the doped GaAs layers competes with conduction from the two-dimensional electron gas confined by the InGaAs quantum well. Photoluminescence measurements at 4 K yield a band-gap energy of 1.30 eV and confirm the transport measurement of carrier density in the InGaAs conducting channel. Analysis of the parallel-conduction process yields channel carrier density and mobility which are consistent with data on strained-layer superlattices (SLS’s) not exhibiting parallel conduction. Comparison of the SSQW and SLS results demonstrates that heavily doped SSQW structures require narrow doping spikes to avoid parasitic current paths. [ABSTRACT FROM AUTHOR]

Hall-effect data between 4 and 300 K on p-type strained quantum well structures in the InGaAs alloy system show pronounced effects due to the strain-induced splitting of the heavy- and light-hole valence bands. As a function of biaxial compression in the range 0.5–1.4%, the 77 K mobilities increase monotonically by a factor of ∼5, as does a high-temperature activation energy which is found to be nearly equal to the predicted strain splitting. [ABSTRACT FROM AUTHOR]

Monolithic vertical cavity surface emitting lasers (VCSELs) on Si are demonstrated. The GaSb multi-quantum well active region embedded in an Al(Ga)Sb half-wave cavity spacer layer enables lasing under room-temperature optically-pumped conditions. The 13% lattice mismatch is accommodated by a spontaneously formed 2-D array of 90° misfit dislocations at the AlSb/Si interface. This growth mode produces very low defect density (∼8×105/cm2) and relaxed materials growth (98%) without the use of a buffer layer. Presented are VCSEL lasing spectra, light-in against light-out curves along with defect density measurements performed by microscopy and etch-pit density. A threshold excitation density of Ith=0.1 mJ/cm2 and a multimode lasing spectrum peaked at 1.62 µm, results from a 3 mm pump-spot size. [ABSTRACT FROM AUTHOR]